Nosema apis is an obligate intracellular parasite belonging to phylum Microsporidia. This para site is known as main causative agent of nosemosis in honeybees especially in the European honeybee (Apis mellifera). Nosemosis can cause queen supersedure, reduction of honey yield and dwindling the population of honeybees. A total number of 54 apiaries were randomly sampled from April to July 2011 and April to July 2012 in North Khorasan province, Iran. Collected samples were examined for infection to N.apis. In the collected bees from 30 apiaries, any Nosema infection was not observed in spring 2011, while of 24 apiaries sampled in spring 2012, 12 (50%) apiaries were infected with N. apis. The seasonal rainfall of spring in 2012 in the study area was 53% higher than the same period of last year. It was concluded that there has been a direct relationship between rainfall and frequency of N. apis infection in apiaries of North Khorasan province.

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